1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) including a back light unit, and more particularly, to a liquid crystal display (LCD) in which an infrared rays (IR) source is used as a back light unit and a multi-touch system using the same.
2. Description of the Background Art
Recently, as development is rapidly made to an information-oriented society, flat panel displays (FPD) having excellent characteristics that are made thin and light and that consume a small amount of power are required. Among the FPDs, liquid crystal displays (LCD) have high resolution, picture quality, and color display characteristics so that the LCDs are actively applied to the monitors of notebooks or desktops.
In general, in an LCD, two substrates in which electric field generating electrodes are formed, respectively, are provided so that the surfaces on which the two electrodes are formed face each other, liquid crystal is implanted between the two substrates, and a voltage is applied to the two electrodes so that liquid crystal molecules are moved by a generated electric field to display an image by the transmittance of light that varies with the movement of the liquid crystal molecules.
Since a common LCD does not emit light by itself but controls the transmittance of light, an additional light source is required.
Therefore, a back light is provided on the rear surface of an LCD panel and the light emitted from the back light is incident on the LCD panel to control the amount of light in accordance with the arrangement of liquid crystal and to display an image.
The back light is divided into a direct light type back light provided under the LCD panel to directly illuminate the entire surfaces of the substrates and a side light type back light provided on one side or on both sides of the LCD panel to reflect light by a light guide plate and a reflection plate to diffuse the reflected light.
Here, in the direct light type back light, since the light emitted from a lamp is emitted to the front of the LCD panel, the light guide plate is not required and a plurality of lamps can be used. Therefore, since the light use efficiency of the direct light type back light is high, the direct light type back light can be easily managed, and the size of a display surface is not limited, the direct light type back light is used for a large screen LCD.
A cold cathode fluorescent lamp (CCFL) in which the light emitted from a cold cathode fluorescent tube is reflected by the reflection plate and a milk-white scatter plate is provided on the reflection channel of the light so that the light locally having uniform illumination illuminates the LCD has been used for the LCD.
However, since the thickness of such a back light cannot be made small so that the LCD becomes complicated and enlarged, recently, a technology, in which a light emitting diode (LED) that consumes a small amount of power and that has high response speed and a semi-permanent life is used as a bipolar electrode device that emits light only when current flows for a surface light source so that the back light is made thin and brightness is improved, is suggested.
The conventional back light unit using the LED light source and the LCD to which the back light unit is applied will be schematically described as follow with reference to FIGS. 1 and 2.
FIG. 1 is a plan view of a conventional back light unit consisting of a plurality of R, G, and B LEDs.
FIG. 2 is a schematic sectional view of an LCD including the conventional back light unit consisting of the plurality of R, G, and B LEDs.
As illustrated in FIG. 1, a conventional back light unit 61 includes LED light sources 63 each consisting of a plurality of red (R), green (G), and blue (B) LEDs 63R, 63G, and 63B, which are repeatedly arranged under the back light unit 61 in column and row directions.
The LCD to which the back light unit having such a structure is applied will be described as follows with reference to FIG. 2.
As illustrated in FIG. 2, the LCD to which the conventional back light unit is applied includes the back light unit 61 in which the LED light sources 63 each consisting of the plurality of red (R), green (G), and blue (B) LEDs 63R, 63G, and 63B are arranged and a diffusion sheet 11, a prism sheet 13, and an LCD panel 30 provided on the back light unit 61 to secure a desired view angle.
Here, a reflection plate (not shown) for preventing light from leaking is provided under the LED light source 63.
In addition, the LCD panel 30 includes a lower array substrate 311 on which a switching device for driving the LCD panel is formed, a color filter array substrate 41 on which an image is displayed by driving the switching device, and a liquid crystal layer (not shown) provided between the lower array substrate 31 and the color filter array substrate 41 to control the transmittance of light while moving in a certain direction in accordance with an electric field direction.
On the other hand, a touch panel 51 is attached onto the LCD panel 30 so that a display to which the touch panel 51 is applied is realized.
On the other hand, according to another embodiment of the conventional art, a multi-touch system using the LCD to which the touch panel is applied will be described as follows with reference to FIGS. 3 to 5.
FIG. 3 is a schematic view illustrating the conventional multi-touch system in which infrared (IR) rays LED modules and cameras are arranged.
FIG. 4 is a schematic view illustrating the touch sense image seen from a first camera when the multi-touch system of FIG. 3 operates.
FIG. 5 is a schematic view illustrating the intensity of an IR light source when the IR light source on the side of the conventional multi-touch system is applied.
As illustrated in FIG. 3, the conventional multi-touch system includes the LCD to which the touch panel 51 is attached, the plurality of first to fourth cameras 71A, 71B, 71C, and 71D provided at the edges, the first to fourth IR light source modules 73A, 73B, 73C, and 73D provided between the two adjacent cameras.
As illustrated in FIG. 4, in the conventional multi-touch system having the above structure, the IR LED modules operate as the back light so that the first to fourth cameras 71A, 71B, 71C, and 71D sense a touch object 75a in a dark environment.
At this time, for the first camera 71A to sense touch, among the first to fourth IR LED modules 73A, 73B, 73C, and 73D, only the first and second IR LED modules 73A and 73B are to be turned on and the third and fourth IR LED modules 73C and 73D are to be turned off.
In the above structure, when the first camera 71 senses the touch object 75a, as illustrated in FIG. 5, since the first and second IR LED modules 73A and 73B operate to the first camera 71A as the back light, the first camera 71A displays the touch object 75a where IR reflection is generated to be black and displays the remaining part 75b directly incident on the first camera 71A without reflecting IR to be white to sense the touch object 75a. 
The conventional LCD and the multi-touch system to which the conventional LCD is applied have the following problems.
As illustrated in FIG. 5, in the conventional LCD and the multi-touch system to which the conventional LCD is applied, the first camera 71A and the first IR light source 73A are all positioned on the sides so that the directional vector components of the first camera 71A and the first IR light source 73A are not the same horizontal line but are close to similar horizontal lines through the control of the positions of the first camera 71A and the first IR light source 73A.
Due to such a structural defect, the light of the IR light source positioned on the side is directly incident on the camera on the side or is reflected and incident, which severely deteriorates the operation of the touch system.
Therefore, the image of the camera can be distorted by an extremely small error to cause an erroneous operation. In addition, when a product is actually manufactured, it is difficult to correctly set the product.
Furthermore, like in the conventional art, in the technology of providing the IR light source on the side, as illustrated in FIG. 5, the intensity of IR light is reduced away from the IR light source module 73A. Therefore, the intensity of the reflected light of the touch object is not uniform so that the efficiency of the system deteriorates.